1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to an apparatus for compensating for corner focus and brightness in a cathode ray tube (CRT).
2. Background of the Related Art
Generally, a CRT is an image display device used in a monitor for a computer or a TV. The CRT includes an electron gun for emitting three colored electron beams of red(R)/green(G)/blue(B), a screen for displaying light by colliding the electron beams emitted from the electron gun against a phosphor plane, a shadow mask for dividing the three colored electron beams emitted from the electron gun, and a deflection yoke for deflecting the electron beams emitted from the electron guns into a given place of the screen which acts as an image display plane.
Since the image display plane has a curved surface structure, the range of the electron beams depends on each position. For example, the range of the electron beams in a central portion is different from that in a corner portion. Accordingly, there results in that focus in the corner portion of the image display plane is not correct and brightness is deteriorated. To solve these problems, there has been suggested an apparatus for compensating for focus error in the corner portion and brightness deterioration.
As shown in FIG. 1, a related art apparatus for compensating for corner focus and brightness in a CRT includes a CRT 1, a parabola signal generator 2 for generating a parabola signal by modulating input vertical and horizontal driving pulses, a focus compensator 3 for compensating for corner focus by amplifying the parabola signal input from the parabola signal generator and outputting the amplified signal to a first grid electrode G1 of the CRT 1, and a brightness compensator 4 for compensating for corner brightness by amplifying the parabola signal input from the parabola signal generator 2 and outputting the amplified signal to a fourth grid electrode G4 of the CRT 1, a fly back transformer 5 for supplying high voltage of 24 KV to an anode electrode of the CRT 1, an error amplifier 6 for amplifying errors of an output voltage of the flay back transformer 5 and a reference voltage, and a +B converter 7 for converting the output of the error amplifier 6 to a direct current voltage for operating the fly back transformer 5.
The operation of the aforementioned related art apparatus for compensating for corner focus and brightness in a CRT will be described below.
The parabola signal generator 2 receives vertical and horizontal driving pulses and outputs the parabola signal containing a direct current component and an alternating current component.
Subsequently, the focus compensator 3 amplifies the parabola signal of the parabola signal generator 2 to a voltage level required to compensate for focus and inputs the amplified signal to the fourth grid electrode G4 so that corner focus of the CRT 1 is compensated.
The brightness compensator 4 amplifies the parabola signal of the parabola signal generator 2 to a voltage level required to compensate for brightness and inputs the amplified signal to the first grid electrode G1 so that corner brightness of the CRT 1 is compensated.
Meanwhile, the fly back transformer 5 transforms the direct current voltage from the +B converter 7 and supplies high voltage of 24 KV to an anode electrode of the CRT 1.
At this time, the fly back transformer 5 has an operational frequency characteristic that its high voltage output is not always maintained to be constant, thereby causing errors. Therefore, the error amplifier 6 amplifies errors of a feedback voltage from the fly back transformer 5 and a reference voltage and inputs the resultant value to the +B converter 7.
Then, the +B converter 7 converts the output of the error amplifier 6 to a direct current voltage required to operate the fly back transformer 5 and supplies the converted value to the fly back transformer 5.
Consequently, an image for which focus error and brightness deterioration are compensated by the aforementioned operation is displayed on a screen of the CRT 1.
However, the related art apparatus for compensating for corner focus and brightness in a CRT has several problems.
Since there are provided for separate compensators to compensate for corner focus and brightness, the manufacturing cost and power consumption increase. Furthermore, in case of a large sized CRT, corner focus and brightness are accurately compensated, thereby deteriorating picture quality.